[GDB stub]first version
[bsp]add gdb support for stm32f4xx
[libcpu]am335x edit vector

vector_undef and vector_dabt
[bsp]add gdb support for BBB
Revert "[bsp]add gdb support for BBB"

This reverts commit a966dd3c3802198cf84adbd8aef08d9206e256ce.
[bsp]add gdb support for BBB